The long-term objective of this grant is to further understand the cellular mechanisms underlying the pathophysiology of both acute and chronic pain states. The neurophysiological mechanisms underlying the transmission and processing of nociceptive, or painful, stimuli within the central nervous system remain poorly understood. Multiple neurotransmitter system are thought to be involved in the transmission of pain signals, including but not limited to those mediated by glutamate and serotonin (5- HT). Although substantial evidence exists implicating glutamate as the principle neurotransmitter responsible for excitatory transmission, the direct and.or regulatory effects of the 5-HT system on the glutamatergic system are well defined. The overall purpose of this project is to help further define the interactions between the glutamatergic and 5-HT transmitter systems in the spinal chord so as to obtain a clearer understanding of the processes that regulate nociceptive afferent neurotransmission. To investigate how glutamatergic neurotransmission is regulated by 5-HT, an in vitro preparation will be used. Pre-synaptic stimulation is achieved by stimulating the dorsal root and post-synaptic whole-cell recordings are made from visually identified single neurons in the substantia gelatinosa using the patch clamp technique. Briefly, a thin transverse section of spinal cord with dorsal roots attached is obtained from post-natal rat pup. The spinal cord slice is then superfused in an extracellular bath solution containing selective agonists and antagonists for specific 5-HT receptor subtypes while recording dorsal root-evoked post-synaptic events. Proceeding in this manner will enable us to identify which 5-HT receptor subtypes modulate glutamatergic transmission. Once the receptor subtypes are identified, the site(s) of action, pre-and/or post-synaptic, will be identified. The results will hopefully provide new insights into the mechanisms of pain transmission as well as suggest novel methods for providing analgesia in both the acute and chronic setting.